Introduction: Lowe syndrome (LS), also known as oculocerebrorenal syndrome of Lowe (OCRL), is a rare X-linked condition characterized by congenital cataracts, defective renal tubule cell function, muscular hypotonia and variable degrees of mental retardation. Patients with LS require frequent surgery, some of which are associated with a severe haemorrhagic risk, such as scoliosis reduction, hip surgery, or eye surgery. In a recent retrospective clinical survey of French LS patients, we observed an abnormal rate of haemorrhagic events, some of which had dramatic outcomes. LS is caused BYMUTATIONS in the OCRL gene, which encodes OCRL, an inositol polyphosphate 5-phosphatase. The preferred OCRLsubstrate is the membrane phospholipid phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2). OCRL also contains a Rho GTPase-activating protein(GAP)-like domain that participates in the regulation of Rho proteins (Rho, Rac, Cdc42), as GTPase-activating proteins or by mediating in protein-protein interactions. PtdIns(4,5)P2 and Rho-dependent signalling play a central role in many important cellular processes, including vesicular trafficking and cytoskeletal organization both of which are very important for platelet function. Thus, modulation of PtdIns(4,5)P2 levels and/or Rho-dependent signalling would be expected to impact platelet function.